Sound recording



April 22, 1941. J. P. LIVADARY SOUND RECORDING 2 Sheets-Sheet 1 Filed Feb. 12, 1938 QDYUQ m- A T TOENE Y -recording and rerecording systems Patented Apr. 22, 1941 SOUND RECORDING John P. Livadary, Los Angelcs, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application February 12, 1938, Serial No. 130,299

20 Claims. (C1.179-100.3)

Thisinvention relates to electro-optical sound wherein sound is directly translated into electrical currents and then recorded on the, sound film, or the electrical currents are produced by other types of modulating devices from one or more records and then rerecorded on a film. The invention in particular, however, relates to a method of and means for controlling the manner of lightimpressing the.film wherein the type of composite or duplex track may be dependent upon the amplitudes or range of the original sound waves.

An object of this invention, therefore, is to more'efiiciently record sound regardless of the amplitude range thereof.

Another object of the invention is to increase the amplitude limits of the sound track by reducing or lowering the lower recording limit.

A further object of the invention is to automatically vary the manner and form of lightimpressing the film simultaneously with the amplitude control of the modulating currents during the transition period from one manner and form of recording to another.

A further objectof the invention is to reduce the noiselevel of a standard duplex sound track.

A further object of the invention is to control the input to, and consequently the output of, a monitoring element of a'recording system to correspond with the light amplitude variations actually being impressed upon the sound track portion of the film to provide a faithful indication thereof.

There are several types of sound recording systems, and sound records produced thereby, known in the art, the present invention relating to a type wherein a double-hump or duplex type of soundtrack is made. In the present system a double-V light beam is vibrated in the direction of' the film in accordance with the instantaneous values of the sound waves being recorded, the inner edges of the Vs moving transversely of the film and oppositely to one another to form two substantially identical out-of-phase traces on either side of the central line of the sound track portion of the film. At times ,of no signal, two bias traces are produced at the center of modulation of the respective traces, these bias lines appearing as transparent portions on the final print, one edge of each of these bias lines being produced by an effective edge of a pair of outside shutters oppositely actuated by the envelope of the currents being recorded. These are noise reduction shutters, since at times of no signalthe shutters block off the light from the sound track (except for the bias lines), and uncover it in accordance with theamplitude of the traces being'impressed thereon, the center or. zero lines of the two traces always remaining parallel to the edges of the film. .L'liis system is well known as the standard type of duplex variable area recording, and provides nigh-quality sound records.

The present invention contemplates increasing the recordable amplitude range or" the sound track portion of film when employing this type or recording by varying or interchanging single and double trace recording in accordance with me amplitude of the sound Waves being recorded. The present specification discloses a method of and means for controlling the changeover from a single trace to a double trace and vice versa without interfering with the amplitude which will be reproduced from the film. Although the changeover may preferably be made curing silent portions of the sound being recorded, and may be done within a period corresponding to the length of one frame, nevertheless it is possible to actually change over during the actual light impressing of the film. There is also disclosed in the present invention a control system for certain other elements such as the visual monitor to provide the proper readings during the recording of either form of track. fhe present invention also provides a method of and means for reducing the normal ground noise level of the film, thus, making possible the recording of lowersound levels.

Although the novel features which are believed to be characteristic of this invention ,will be pointed out with particularity in the claims appending herewith, the invention itself, its 'obj ects and advantages, the manner of its organization and the mode of its operation willv be better understood by referring to the following description read in conjunction with the accompanying drawings forming a part thereof, in which:

Figure 1 is a combination schematic circuit drawing and a diagrammatic showing of the elements embodying the invention;

Figure 2' shows a sound track positive print made inaccordance with the invention; and

Figure 3 is a graph illustrating the sound levels on the film of Fig. 2.

Referring now particularly to Fig. l, the standard type of variable area duplex sound recording system is shown in the upper righthand corner of the drawing, in which light rays are generated by. a source shown by lamp 5, collected by a lens 6, defined by an aperture 1 in a mask 8 and also by noise reduction shutters 9, and projected by a lens [0 upon a mirror H of a galvanometer i2 shown diagrammatically The light is reflected from the mirror II to a mask l4 having a longitudinal slit l5 therein the light emerging from the slit being projected by objective lenses 16 onto the sound track portion of a film H advanced in any manner well known in the art. This portion of the system one-half the light beam from the film l1.

pilot lights 28 and 29 may be distinguished by,

is well known and produces the double-hump or duplex type of variable area track as shown in the upper portion of Fig. 2.

The present invention involves as one of its phases a modification of the light beam between the light source 5 and the film H, which, as shown, is made at a point adjacent the slit |5 between the mirror H and the slit mask M. The variation made in the light beam is to either eliminate one-half of the beam as itimpinges upon the mask |4 or to permit the full width of this beam to impinge thereon. The elimination is made by means of a pointed shutter attached to the armature of an electro-magnetic solenoid relay 2|, the armature also being connected to a dashpot 22 for timing the movement of the shutter 20 when the solenoid 2| is energized and de-energized. The solenoid is energized over a pair of conductors 23 across which is connected a voltmeter 24 for indicating the exact voltage being impressed on the solenoid.

Energy for the conductors 23 is supplied by any suitable source such as a battery 26, the voltage supplied to the relay 2| being controlled by a variable resistance 21 in one of the conductors 23. Also connected across conductors 23 is a pilot light 28 which is energized simultaneously with .the energization of solenoid 2| and thus indicates that the shutter 20 is in the upper position to permit the full width of the beam to pass through the slot I5. When the solenoid is de-energized, this fact is indicated by a second pilot light 29 which is connected to one of the conductors 23, and, through a conductor 3| and switch blade 32, to battery 26. Thus the switch blade 32 in its lower position causes the energization of the solenoid 2| and the pilot light 28, while in its upper position causes the energization of the pilot light 29. Thus actuation of the switch blade 32 to its lower position allows the full beam width to impinge upon the film I1 and the positioning of the switch blade 32 in its upper position blocks off The different colors or by indicia adjacent thereto.

For actuation of. the galvanometer |2 current variations corresponding to sound waves to be recorded are taken from the output of an ampliher 34, the input of which is connected to the output of a master amplifier 35 through a variable attenuation network represented by resistance elements 38. Sound currents may be supplied to the amplifier 35 from one or more pickups illustrated at 36, 31 and 38, these pickups being some form of translating devices, such as microphones, disc or film reproducers. The individual outputs of these pickup units are amplified by respective amplifiers 39, and 4|, controlled by respective potentiometers 43, 44 and 45, and then combined into a single channel 42, the combined output being control-led by a master potentiometer 46. These potentiometers are customarily called mixing pots.

The circuits just described, except for resist-v ances 38, illustrate the usual recording circuits from one or more pickup devices to the galvanometer l2. Also employed in the usual sound recording or rerecording system are monitoring units such as a loudspeaking system and a visual amplitude meter which audibly and visually indicate the levels of the sound being impressed upon the galvanometer. The present invention utilizes these monitoring aids, one of which is shown as a loudspeaker 48 with its amplifier 49, and the other as a met-er 5| and its amplifier 52, the meter shutters 9 at times of no signal.

5| being either of the mechanical type or one employing a series of neon lamps. In the operation of the usual recording system a mixer controls the proportion of the outputs of pickups 36, 31 and 38 by pots 43, 44 and 45, as indicated by the loudspeaker 48. He also controls the combined amplitudes impressed on the galvanometer by master pot 46 as indicated by the meter 5|. Thus, ordinarily the speaker 48 and meter 5| are permanently connected directly to the main buses 56. For the purpose of this invention, however, the loudspeaker 48, through its amplifier 49, always remains directly connected to the buses 56 over conductors 53, while the visual meter 5|, through its amplifier 52, is connected to the buses 56 over conductors 59. and through a double-pole switch 60. When the switch 60 is in its upper position, the meter 5| is directly connected to the buses; but when in its lower position, an attenuation pad 62 is interposed in the meter circuit.

Referring now to the variable attenuator 38 mentioned above, the insertion thereof in the galvanometer circuit is dependent upon the actuation of a solenoid relay 63, which, when energized, moves its armature 64 toward the left thereby inserting the impedance in the circuit. Upon de-energization of the relay 63, a tension spring 66 removes the impedance 38 from the circuit, as shown. The timing of the operation of the relay 63 is controlled by a mechanical filter composed of the tension spring 66 and a d ashpot element 61. Although onespecific form of a variable timed attenuator is illustrated, it is to be understood that a purely electrical delay pad may be employed at this point in any manner well known in the art. The solenoid 63 is energized at will over a pair of conductors 68 connected by switch blade 32 to the source of energy 26. Thus with the switch blade 32 in its lower position not only will the relay 2| and pilot light 28 be energized, but also the relay 63, so that when the mask 20 is removed from the light beam the resistances 38 will be inserted in the galvanometer circuit. Actuation of the switch blade 32, however, also actuates double-pole switch 60, since switch 60 is mechanically connected to switch 32, as shown by the dotted line 10. Thus with the switch blade 32 in its lower position, energizing relays 2|, 63 and light 28, the pad 62 is inserted in the circuit of the meter 5|. On the other hand, with the switch blade 32 in its upper position, the relays 2| and 63 are de-energized, the pilot light 29 is energized, and the meter 5| is directly connected to buses 56. The purpose and reasons for thus varying these circuits will now be explained.

The present system functions to increase the absolute recording range of a duplex film and is particularly advantageous where there is being recorded music and/or dialogue intermittently, in which the music covers a wide range of amplitudes and the dialogue is interposed and might even fall below the lowest level of the music. The invention also functions to reduce ground noise at times of no signal as well as at times when the signal is at a low level. Referring now to Fig. 2, showing a sound track portion of a motion picture film made with the invention, at the top of the drawing are the usual two so-called bias lines 12 and 13. These lines are produced by the inner edges of the V's oi the light beam impressed on the mask l4 and by the effective edges of the That is, the shutters mask the light beams from the areas 14 and I5 of the film, except tor that light which "produces the transparent portions -72 and I3. This track of course, is produced with the mask 20 in its upper position.

Now, as the actual signal is impressed upon the galvanometer [2, a rectifier (not shown) suppliescurrent corresponding to the envelope of this signal to a magnetic element 9, which operates the noise reduction shutters 9, separating them .in accordance with the amplitude of the signal and thus permitting the modulation traces J1 and 78 to be effective on the sound track portion of the film. As the amplitude of the signal decreases, the shutters come togetherand again block out the light from the him, as shown in Fig. 2 at 1.9 :and 80. If the modulations continue I to decrease to zero, the bias lines would again be formed as shown at 1 2 and 13. This type of trackhas many advantages, suchas that each trace supplements. the other during reproduction,

thus providing maximum modulation of the sound track area. Also, each trace is separately reproducible as a true reproduction of the original signal so that any slight imperfections in one trace will not eliminate or unduly distort the signal. It is well understood that the chief source of ground noise is the non-uniformity of the clear portions .of the sound track. When the amplitude level of the signal output from a reproduced film is above the ground .noise level sufiiciently to blanket the noise, reproduction is satisfactory. But at times of no signal this noise may be .annoying and there is a point in the signal am.- plitude level below whichit is not desirable to record because of the predominance of the reproduced noise with respect. to the reproduced signal. This is the point. where the amount of light passing through the clear sections of the film would be large compared to the variations in light caused by the small amplitude .of the traces l1 and 18. This is well known as the signal to noise ratio and, where this ratio is high at points 11 and 18, itis low at points of low modulation, such as points M and 82.

The present invention, therefore, contemplates lowering the satisfactory minimum recording limit, that is, it permits the recording of a lower signalamplitude with respectto a definite upper limit. In brief, this is accomplished by removingor eliminating. the recording :of one of the I traces suchas 11, and.simultaneouslyincreasing the amplitude of the other trace to'compensate for the decrease in variations, of light upon the reproducing photocell caused. by the, elimination.

Thus, the signal to noise ratiomay be substanll tially doubled and the film track portion is therefore given a wider recordable amplitude range and may thus more faithfully represent the :true variations in amplitude of the original sound as well as representl the proper dialogue level with respect to the music. It also maintains the dramatic effects since the .mixerls not required to. squeeze the volume; that is, raise the lower levels or reduce the higher levels to accommodate the volume range of the film.

-To further illustrate the operation of the invention, particularly with respect to the control thereof, let us assume that an overture or a dramatic musical selection is being recorded in which there is a wide range in amplitudes, the pickups 36, 31 and 38 being microphones and placed atstrategic points on the set. The mixer at his controls listens to the output of loudspeakerfhl to generally determine the recording amplitude and particularly to obtain the proper 15 musical combination effect from the various microphones. Similarly, he watches the meter 5| toaccurately determine the level which may be properly impressed upon the galvanometer [2. We may assume that both traces are being impressed .on the film, which means that switches 32 and 60 are in their lower positions so that .pad 62 is in the circuit of meter 5| and the resistances 38 are in the galvanometer circuit.

Now as the amplitude level decreases, {the meter 5| will indicate a certain level of modulations being impressed on the galvanometer 12 at which it may be considered that the signal to noise ratio may be too low for satisfactory reproduction. This means, of course, that the traces H and 18 have reached an amplitude where the amount of varied light is low compared with the total light which would be transmitted through the film. At this point the mixer may manually operate the switch 32 from its lower position to its upper position allowing the mask 20 to intercept one-half thealight beam being impressed on the film, thus eliminating one of the traces, such as 11 shown in Fig. 2. The actuation of the switch 32 in this manner will extinguish light 29 and energize lamp 28 to indicate that this change has been made and will simultaneouslymove the switch 60 to its upper position to remove the .pad 62 from the meter circuit and connect the meter directly to buses 56. The moving of the switch 32 to its upperposition also de-energizes solenoid 63, which allows the spring 66 to remove the resistances 38. from the galvanometer circuit. These adjustments all occur simultaneously, that is, the shutter moves into the light beam and the resistances 38 are removed Within the same predetermined time interval dependent upon the adjustments of the timing elements described above.

As shown in Fig. 2, this time interval is substantially the time it takes one frame to pass a given point which will be 2%; second for standard film. As one trace is eliminated by the insertion of the shutter 20, the amplitude level of the currents} bein impressed on the galvanometer l2 are increased. The elimination of the trace is illustrated in Fig. 2 by the broken line 32 which shows, from the point a to the point 1), how the trace 1'! is removed from the film. Also from the point etc the point d, the trace 18 is shown increasing in amplitude to substantially twice its former value so that as far as the reproducible output of the film is concerned, the traces at points a and c produce the same amplitude of output as the single trace 13 at point d. After the changeover has been made, it is then possible for the amplitude of the single trace to be varied as the volume of the signal varies, a full amplitude trace being shown at point e. It is to be noted that although the output volumes of the film at point ac and point d are the same, the signal to noise ratio is substantially twice its value at point (I as at. point a-c. Thus the trace 18 may be reduced to an amplitude such as shown at 'c which will reduce its output volume to onehalf of its volume at d without increasing the signal to noise ratio beyond what it was when both traces were effective at this lower amplitude. Thelower recording limit is thus lowered.

Now, if the volume increases so that the single trace is at full modulation, the switch 32 may then be thrownlto its lower position to remove the mask 20 and allow both traces to become effective on the film. When this occurs, of course, the reverse actionsare :brought about so that the retual variations in the input signal,

sistances 38 are inserted into the circuit to compensate for the introduction of both traces, and the pad 62 is placed in the visual meter circuit.

During the above-mentioned circuit variations,

the mixer is at all times aware of the exact amplitude being actually impressed upon the galvanometer l2 regardless of whether or not the resistances 38 are in or out of the circuit. This prevents overand under-modulation of the sound track. However, even though there is a change in the amplitude of the currents to the galvanometer, the audible monitor still indicates the ac- In other words, the meter M is at all times related tothe variations in current impressed on the galvanometer l2, while the speaker 48 is at all times related to the variations at the pickups 36, 37 and 38. The meter 5| follows the input to the galvanometer by the insertion and elimination of the pad 62 from the meter circuit. For instance, say the volume of the signal has reached the level at which changeover is brought about. At this point the resistances 38 may be cut out of the circuit, thus increasing the amplitude being impressed upon the galvanometer l2. Simultaneously, the pad 62 is removed from the meter circuit to permit the meter to read or indicate the increase in amplitude caused by the removal of the resistances 38. Thus, the meter 5| always indicates the actual amplitude of the currents being impressed on the galvanometer and prevents overloads of either the single trace or the double trace. The above describes a recording system having all the advantages of a double duplex trace, but which increases the recordable. range thereof without interfering with the recording controls or operation. Thus, modulations of a much lower amplitude can be impressed on the film to increase the total volume range of the sound track portion of standard film.

For another illustration of the variations in the above levels, reference is made to Fig. 3 in which the graph represents percentage modulation with respect to time or number of frames. This is, considering the entire sound track as 100% of the available modulation area, each trace represents 50% modulation thereof and the distance from zero to point I may thus represent the bias lines 12 and 13 of the film in Fig. 2. An increase in modulation to maximum is shown at points g and h which represents 50% modulation of each half of the entire track. This modulation may then be decreased to shown at points i and 7', at which time, if desired, the changeover may be made wthin one recording frame. This time of operation is represented by the distance between the points 2 and k or between 7' and Z wherein one trace is entirely eliminated and the remaining trace is increased in amplitude to 20% modulation. Thus, the output from the film at points i and 7' is the same as k and Z. The lower trace is shown as continuing to a full 50% modulation at m and then to any other value as shown at q.

Although points of 10% modulation have been taken as changeover points for purposes of illustration, it is to be understood that changeover may occur at any level when shifting from one to two traces and at any level under 25% for each trace when shifting from two traces to one trace. Of course, the shift may always be made at a silent period, affecting the sound track only in that one bias line is removed. It is also to be understood that although the time required to make the changeover has been shown to occur within one frame, this time may be shortened, or

varied differently for each element by adjustment of the time elements 22 and 61. A further modification within the scope of this invention is that instead of actuating the switches 32 and 60 manually, these switches may be operated automatically by a marginal relay controlled by the currents to the galvanometer. Also, it is to be understood that should the loudspeaker 48 be connected to amplifier 34, a pad similar to pad 62 may be employed and shifted in and out of the speaker circuit when the changeovers are effected.

I claim as my invention:

1. A sound recording system comprising a source of light rays, means for varying the form of said rays, means for projecting said rays onto a motion picture film, means for vibrating said rays in accordance with sound waves to be recorded, means for controlling at will said form varying means, and means for simultaneously controlling the amplitude of vibration of said rays being impressed on said film.

2. A sound recording system comprising a source of light rays, means for forming said rays into a plurality of beams, means for projecting said beams onto a motion picture film, means for vibrating said beams in accordance with sound waves to be recorded, means for varying at will the number of said beams being impressed on said film, and means for simultaneously varying the amplitude of the beam orbeams being impressed on said film, said last-mentioned means increasing the amplitude of said beams impinging on said film simultaneously with the elimination of said beams from said film,

3. A sound recording system for the electrooptical recording of sound on film comprising means for producing a plurality of light beams, means for projecting said beams on said film, means for modulating the lengths of said beams transversely of said film in accordance with sound waves to be recorded, and means for decreasing the length of one of said beams to zero with respect to said film during modulation thereof.

4. A sound recording system in accordance with claim 3 in which the length of one of said beams being impressed upon said film is increased in proportion to the decrease in length of the other of said beams being impressed upon said film.

5. A sound recording system for electro-optically recording sound on film comprising means for modulating the length of a plurality of narrow light beams, means for impressing said beams on said film, the length of said beams being substantially equally increased and decreased for the same variations in sound wave amplitudes, there being a predetermined maximum length and minimum optimum length therefor, and means for impressing on said film the variations in only one of said beams While eliminating the other of said beams from said film for amplitudes below a predetermined amplitude level.

6. A sound recording system comprising means for producing a plurality of narrow light beams, the length thereof varying in accordance with the amplitude of sound waves to be recorded, said beams having a maximum predetermined length and an optimum minimum length, the maximum length being determined by the width of the sound track portion of the film, and the mini mum length being determined by permissible film ground noise, means for eliminating one of said beams when its length is below said minimum length, and meansfor simultaneously increasing the length of the other of said beams as the length of the first beam is eliminated.

7. A sound recording system in accordance with claim 6 in which the period of elimination of one beam and the period of increase in said other beam occur over substantially the same longitudinal portion of the film.

8. A sound recording system in accordance with claim 6 in which the period of elimination of one beam and the period of increase in said other beam occur over equal time intervals.

9. A sound recording system comprising means for producing a plurality of light beams, each of said beams varying in accordance with sound waves to be recorded, means for modulating said beams, means for impressing currents varying in accordance with sound waves upon said modulating means, means for eliminating one of said beams from impression upon a film, and means for varying the attenuation of said currents in accordance and simultaneously with the elimination of another of said light beams.

10. A sound recording system comprising means for generating currents corresponding to sound waves to be recorded, means for generating a plurality of light beams, means for impressing said light beams upon a motion picture film, modulating means on which said currents are impressed for modulating said light beams in accordance with the amplitude variationsof said currents, means for audibly monitoring said currents impressed on said modulating means, means for visually monitoring said currents as impressed upon said modulating means, means for eliminating one of said light beams from impression upon said film, means for simultaneously varying the amplitude of the currents impressed on said modulating means, and means for simultaneously varying the amplitude of the currents impressed upon said visual monitoring means.

11. The method of producing a constant output sound track during an increase in the light modulation being impressed on said track, comprising impressing a light modulation of increasing amplitude on said track, and simultaneously decreasing the sound track recording area in proportion to the increase in amplitude of said light modulation.

12. The method of increasing the recordable range of a predetermined sound track portion of film having multiple modulations thereon comprising varying the number of modulations in accordance with the signal level being recorded and varying the level of the modulations being impressed on the film in accordance with the number of effective modulations.

13. A recording system comprising an electrical circuit for light modulating a film, a variable attenuator in said circuit, a monitor circuit for indicating the amplitude of the currents in said modulating circuit, an attenuator in said monitor circuit, and means for simultaneously varying said attenuators.

14. A recording system comprising a plurality of means for generating currents corresponding to sound waves, means for combining said currents into a single circuit, means for modulating a light beam with said currents, means for indimeans, the amount or said last-mentioned variations corresponding to said first variation.

15. A standard duplex variable area recording system comprising means for producing a divisionallight beam, a shutter adapted to intercept a division of said beam, electrical means for actuating said shutter, a modulator of said light beam, means for impressing a signal to be recorded on said modulator, electrical means adapted to vary the amplitude of the signal impressed on said modulator, a meter for indicating the amplitude of said signal being impressed on said modulator, electrical means adapted to vary the amplitude of the signal impressed on said meter, and a circuit interconnecting said shutter actuating means, said modulator amplitude varying means, and said meter amplitude varying means, said circuit being adapted to simultaneously actuate all of said means.

16. The method of producing a substantially constant output sound record during certain predetermined variations in the light modulation being recorded, said record having a varying output during certain other variations in said light modulation being recorded, comprising impressing a light modulation of varying amplitude on said record and simultaneously varying the effective recording area of said record during certain of said amplitude variations in said light modulation, said record thereby having a substantially constant output when this portion of said record is reproduced, while maintaining the effective width of said recording area constant during other amplitude variations of said light modulation, said record thereby having a varying output when said portion of said record is reproduced. a

17. A sound recording system comprising a source of light rays, means for varying the form of said rays, means for varying said rays in accordance with variations in sound waves, means for controlling the operation of said form varying means, said last-mentioned means simultaneously controlling said other variations in said rays, and means connected to said form varying means and said ray varying means or at least one thereof for controlling the rate of change in the variations of at least one of said varying means.

18. The method of recording a sound record comprising impressing a light beam on said rec- 0rd, said beam varying in form and amplitude, and controlling the rate of change of said variations in form and amplitude so that said variations in form occur over the same time interval as said variations in amplitude.

19. A recording system comprising an electrical circuit for light modulating a film, a variable attenuator in said circuit, a monitor circuit for indicating the amplitude of the currents in said modulating circuit, an attenuator in said monitor,

circuit, and means for varying the attenuator in said monitor circuit in accordance with the amount of variation made in the attenuator in said modulating circuit.

20. A sound recording system comprising a source of light rays, means for varying the form of said rays, means for projecting said rays onto a motion picture film, means for vibrating said rays in accordance with the amplitude of sound waves to be recorded, means for manually controlling said form varying means, and means for manually controlling the amplitude of vibration of said rays being impressed on said film.

JOI-DT P. LIVADARY. 

